The contract format may be altered by the exchange without prior notification to the broker.
It appears that the new weekly contract format replaces month names with numeric values, as seen below:
Old Format: BANKNIFTY-24-J-17-48000-CE
New Format: BANKNIFTY-24-1-1748000-CE
This modification in format has been noted in Nifty and other contracts as well. We plan to verify this with the exchange for confirmation, but it currently looks like the format has changed.
This is another reason why we depend on instrument keys, ensuring that any unannounced changes do not impact our system and our customers.